This invention generally relates to air recovery electrochemical cells.
Batteries are commonly used electrical energy sources. A battery contains a negative electrode, typically called an anode, and a positive electrode, typically called a cathode. The anode contains an active material that can be oxidized; the cathode contains an active material that can be reduced. The anode active material is capable of reducing the cathode active material. In order to prevent direct reaction of the anode material and the cathode material, the anode and the cathode are electrically isolated from each other by a separator.
When the battery is used as an electrical energy source in a device, electrical contact is made to the anode and the cathode, allowing electrons to flow through the device and permitting the respective oxidation and reduction reactions to occur to provide electrical power. An electrolyte in contact with the anode and the cathode contains ions that flow through the separator between the electrodes to maintain charge balance throughout the battery during discharge.
An air recovery battery, also known as an air assisted or air restored battery, is a battery that uses air to recharge its cathode during periods of low or no discharge. One type of air recovery battery employs zinc powder as the anode, manganese dioxide (MnO2) as the cathode, and an aqueous solution of potassium hydroxide as the electrolyte. At the anode, zinc is oxidized to zincate:
Zn+4OHxe2x88x92xe2x86x92Zn(OH)42xe2x88x92+2exe2x88x92
At the cathode, MnO2 is reduced to manganese oxyhydrate:
MnO2+H2O+exe2x88x92xe2x86x92MnOOH+OHxe2x88x92
When the cell is not in use or when the rate of discharge is sufficiently slow, atmospheric oxygen enters the cell and reacts with the cathode. Manganese oxyhydrate is oxidized to form MnO2:
xe2x80x83xc2xdO2+MnOOHxe2x86x92MnO2+OHxe2x88x92
During high rates of discharge, air recovery batteries operate like conventional alkaline cell by reducing xe2x80x9cfreshxe2x80x9d (unreduced) MnO2. During low rates of discharge and periods of rest with no current flow, the xe2x80x9cconsumedxe2x80x9d (reduced) MnO2 is restored or recharged by atmospheric oxygen to the fresh state. Since oxygen must reach the MnO2 for recharging, the cathode of the battery must not be wetted completely by electrolyte. If the cathode is soaked with wet electrolyte, air transport properties inside the cathode degrade and recharging of MnO2 is hampered.
In one aspect, the invention features a racetrack air recovery battery having a cathode, an anode, and a separator. The cathode may include manganese dioxide, and the anode may include zinc. The battery can provide good air distribution to the cathode and protection against leakage of electrolyte. The batteries can also be stacked together to provide high capacity or higher voltages.
In another aspect, the invention features a racetrack air recovery battery including a can having a racetrack cross section; a cathode assembly disposed in the can; a bottom portion disposed on an end of the cathode assembly; and anode material disposed in the can. The bottom portion can be a bottom cup. The cathode assembly can include a barrier layer and manganese dioxide. The anode material can include zinc. The can may include a groove. The bottom cup may allow the cathode to make better electrical contact with the can and generally provides protection against leakage of electrolyte. The bottom cup and the groove help provide an air plenum between the cathode assembly and the can to provide good air distribution to the cathode.
In another aspect, the invention features a racetrack air recovery battery including a can having a racetrack cross section; a cathode assembly disposed in the can; anode material disposed in the can; and a seal assembly disposed in the can, the seal assembly including a current collector having a shape that maximizes uniform discharge of the battery. The current collector can extend substantially along a full length of a longitudinal axis of the battery. At least two separate portions of the current collector can extend substantially along a full length of a longitudinal axis of the battery. A portion of the current collector can approximate a triangle. The current collector can provide uniform discharge of the battery for consistent and optimum battery performance.
In another aspect, the invention features a method of assembling a racetrack air recovery battery. The method includes: (a) inserting a cathode assembly into a can having a racetrack cross section; (b) placing anode material in the can; (c) inserting a seal assembly into the can, the seal assembly having a current collector; and (d) sealing the can. The method can further include placing a barrier layer adjacent to the cathode assembly, placing an air diffusion layer around the cathode assembly, and placing a bottom cup on an end of the cathode assembly. The method can include forming a groove in the can. Sealing the can may include mechanical crimping.
The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims.